The methods of fracture prediction based on structural strain analysis and its application

Formation strain can directly affect the generation of structural fractures. According to the magnitude of structural strain, the location and intensity of structural fracture development can be predicted, and the chief fracture development areas in the study area can be divided. This paper takes the fourth member of the Yingcheng formation (referred to as the YING-4 section) in the Xuzhong area of the Xujiaweizi rift in the Songliao basin as the research object. Based on establishing a detailed 3D structural model of the study area, we used the “structural restoration” method to restore the paleo-structure of the study area and calculated finite strain values to predict the planar distribution of structural fractures. The research shows that the YING-4 section in the study area mainly includes three fracture-making periods, namely the end of the Yingcheng formation, the Quantou–to–Qingshankou formation, and the Nenjiang formation. Among them, the tectonic deformation at the end of the Yingcheng formation and the Quantou–to–Qingshankou formation is relatively strong, which is the main formation period of the fracture. The study area is divided into three types of fracture development zones according to the relationship between strain size and test gas production. Type I fracture development zone has been verified by well-drilling, indicating that the prediction results of fractures using structural strain are reliable. Type Ⅱ fracture development zone can be used as an important direction for the next step of deep natural gas exploration. Type Ⅲ fracture development zone has low productivity, and the fractures have limited effect on reservoir reconstruction.